Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$79.87	12.330%	$89.718	$89.72	$89.70	$89.70
Purchase #2	$206.52	6.435%	$219.8096	$219.81	$219.80	$219.80
Purchase #3	$114.65	12.273%	$128.721	$128.72	$128.70	$128.70
Purchase #4	$105.36	4.367%	$109.9611	$109.96	$109.95	$110.00
Purchase #5	$144.96	8.568%	$157.3802	$157.38	$157.40	$157.40
Purchase #6	$212.71	4.335%	$221.931	$221.93	$221.95	$221.90
Purchase #7	$128.73	3.609%	$133.3759	$133.38	$133.40	$133.40
7 purchase totals =	$992.80		$1,060.8968	$1,060.90	$1,060.90	$1,060.90